The effect of hexagonal boron nitride encapsulation on interlayer interactions in few-layer molybdenum ditelluride.

The encapsulation of few-layer transition metal dichalcogenide (TMD) structures in hexagonal boron nitride (h-BN) is known to improve their optical properties, which is of crucial importance for their applications. In order to study the effect of encapsulation on interlayer interactions in few-layer TMDs the low-energy Raman scattering spectrum of bi- and trilayer MoTe$_2$ is investigated. Three breathing modes are observed in the spectra of these few-layer MoTe$_2$ structures deposited on/encapsulated in h-BN as compared to one breathing mode for the flakes deposited on an SiO$_2$/Si substrate. Conversely, the shear mode is not affected by changing the substrate. We relate the emerged structure of breathing modes to the interaction of MoTe$_2$ with the h-BN substrate. The interaction slightly affects the energy of the main breathing mode and contributes to the combination modes due to interlayer and layer-substrate interactions. We also show that the h-BN substrate determines the Raman spectrum. The interaction between MoTe$_2$ and the top h-BN layer has a negligible effect on the low-frequency Raman scattering spectrum.